Hi Muffin Top! Step aerobics is certainly safe to do on consecutive days. Especially since you have no problems or injuries to work around. Overtime, any exercise which is done repetitively with no change will cause overuse of the musles, joints, tendons and ligaments. Not only that but your body will get so used to the form of activity that your results will begin to diminish. That's why its recommended to alter your exercise program for both safety and effectiveness.
But if your truly love step over most activities, there is nothing wrong with doing that a couple of more times a week than other activities and or doing it on consecutive days for up to three days but preferrably two (ie: Mon/step...Tues/step...Wed/run...Thurs/step...Fri/eliptical... Sat/kickbox...Sun/off)
I don't think its necessary to lower your step height if the height that you are on causes you no discomfort and keeps you in your training zone. If your thoughts on doing that are simply to keep your joints free from wear and tear, then a different activity would be a better option than changing your step height. I would say that you only need to change your step height if the height that you are on has you gasping for air, or feels awkward, or causes pain in your knees, hips, ankles.
